Having shown the applicability of our zero index condition to general electromagnetic materials, we give an example for another kind of wave. In the theory of elasticity, the equation of motion is a continuous version of the Newtonian equation of motion \({F}=m{a}\)  [1]},
\(\rho \frac{\partial ^{2}{U}}{\partial t^{2}}=-\rho \omega ^2{U}={\nabla }\cdot {\sigma }.\) 
